1. Technical Field
This invention generally relates to spacer assemblies for insulating glazing units and, more particularly, to a spacer assembly having an inner spacer member and an outer spacer member that carries desiccant outside of the inner spacer member. Specifically, the present invention relates to a spacer assembly and a method for fabricating a spacer assembly that uses an inner spacer member that may be formed by existing automated manufacturing equipment in combination with an outer spacer member carrying a desiccant that is wrapped around the outside of the inner spacer member.
2. Background Information
Insulating glazing units are used to reduce heat loss from the interior of a building during cold weather and to retain cooler temperatures inside the building during hot weather. The proper use of insulating glazing units in a building can significantly reduce the cost of heating and cooling the interior of the building.
An insulating glazing unit typically includes at least a pair of outer glazing sheets held together and spaced apart by a spacer assembly. Numerous spacer assembly configurations are known in the art that function to hold the glazing sheets apart from each other while simultaneously forming a hermetically sealed cavity between the glazing sheets and the spacer assembly. Most spacer assemblies include a desiccant to prevent condensation from forming in the sealed cavity.
One known spacer assembly and method for assembling a glazing unit is disclosed in U.S. Pat. No. 4,530,195 that is assigned to Glass Equipment Development, Inc., of Twinsburg, Ohio. The disclosures of this patent are incorporated herein by reference. The spacer assembly disclosed in this patent carries the desiccant inside the metal spacer member. The spacer assembly is formed by cutting frame segments to length and connecting them end-to-end with folding, locking corner keys. As shown in FIGS. 4 and 5 of the patent, a sealant is applied to the three outer sides of the segments by three extrusion nozzles while the segments are linearly aligned. The segments are folded into a polygon and positioned between the glass sheets. The assembly is then passed through a heated roller press to form the insulating glazing unit. This spacer assembly and linear method for fabricating glazing units as well as other similar segmented spacer assemblies that are linearly assembled and then folded have gained success in the art.
Another successful spacer assembly known in the art is sold under the federally registered trademark INTERCEPT® owned by PPG Industries, Inc. of Pittsburgh, Pa. An example of an INTERCEPT® spacer assembly is depicted in FIG. 2 and is indicated by the numeral 8. Spacer assembly 8 includes a metal structural element 10 that has a flat bottom wall 12 and two substantially parallel upwardly extending side walls 14. A stiffening flange or lip 16 may extend from the top of each side wall 14 substantially parallel to the bottom wall 12 and toward one another. A desiccant matrix 18 is disposed inside the metal structural element to adsorb moisture that may enter the cavity 20 of the glazing unit. The outer surface of the metal structural element 10 is coated on three sides with a sealant 22 that bonds the glazing sheets 24 to the spacer assembly 8 and seals cavity 20 from the surrounding atmosphere. U.S. Pat. Nos. 5,177,916, 5,255,481, and 5,351,451 owned by PPG Industries disclose the INTERCEPT® spacer and methods for fabricating the INTERCEPT® spacer. The disclosures of these patents are incorporated herein by reference.
The INTERCEPT® spacer assembly has gained popularity in the marketplace because it can be manufactured with automated manufacturing equipment that produces large quantities of custom-sized spacer assemblies quickly for a low cost. The automated equipment allows the user to create a custom-sized spacer assembly simply by entering the size of the desired glazing unit. The equipment performs the required calculations and controls the machinery to automatically form the required spacer assembly. Companies that use the automated equipment have invested relatively large sums of money (up to $1,000,000) to purchase and set up the automated manufacturing equipment as well as to train employees to use the equipment. Once an automated line is established and the employees trained, the INTERCEPT® spacer is easy and inexpensive to manufacture. The equipment allows that manufacturer to produce up to 2800 frames per work shift. One exemplary method and manufacturing line for automatically manufacturing the INTERCEPT® spacer assembly is disclosed in U.S. Pat. No. 5,295,292 that is assigned to Glass Equipment Development, Inc., of Twinsburg, Ohio. The disclosures of this patent are incorporated herein by reference.
An undesirable aspect common to both of the spacer assemblies discussed above is that the metal spacer member extends essentially entirely between outer glazing sheets 24 and thus transmits heat or cold directly through the edges of the insulating glazing unit. This transmission reduces the insulating effectiveness of the glazing unit because metal is an excellent transmitter of heat and cold. Sealant 22 on the sides of spacer 10 does not create enough of a thermal break between the glass and the metal to be an effective insulator. It is thus desired in the art to provide a spacer assembly that uses one of the spacer assemblies discussed above in combination with another spacer element to create an assembly that provides an insulating member between the metal spacer member and the glazing sheets to improve the overall insulating properties of the insulating glazing unit.
An undesirable aspect of the INTERCEPT® spacer is that a flowable desiccant matrix must be pumped into the interior of the spacer after the spacer is formed. The pumping operation increases the cost of fabricating the spacer. In addition, the flowable desiccant causes the pumps to wear rapidly requiring the pumps to be frequently maintained or replaced. The art desires a method of adding the desiccant to the spacer assembly that avoids the cost of the pumps.
Two other prior art spacer assemblies are depicted in FIGS. 3 and 3A. The spacer assembly 30 depicted in FIG. 3 has been sold under the trademark SUPER U™ by Edgetech I.G. Inc. of Cambridge, Ohio, the assignee of the present application. The SUPER U™ spacer assembly 30 includes a preformed foam spacer member 32 that carries a preformed metal spacer member 34. The spacer assembly is assembled by first forming a frame from the metal spacer member and then cartwheeling the frame into the foam. The foam-metal assembly then must be cartwheeled again to add the adhesive 36 to the outside of foam spacer member 32 before it is sandwiched between glazing sheets 24. A sealant 38 is then added to the sealant channel formed outside foam spacer member 32 and glazing sheets 24.
The prior art spacer assembly 40 depicted in FIG. 3A is similar to spacer assembly 30 but is used to hold a delicate, center-lite art glass between a pair of outer glazing sheets 24. Spacer assembly 40 also has been sold under the trademark CUSHION EDGE by Edgetech I.G. Inc. of Cambridge, Ohio, the assignee of the present application. The foam spacer member 42 is extruded in its final shape during manufacture and must be sized to fit the art glass 44 and to form the desired spacing between glazing sheets 24. A layer of pressure sensitive adhesive 46 is disposed in the U-channel to hold the position of the art glass 44. Spacer assembly 40 further includes a vapor barrier 48 and sections of adhesive 49 that connect assembly 40 to glazing sheets 24.
Although spacer assemblies 30 and 40 are functional, it is difficult to retrofit an existing automated INTERCEPT® spacer assembly line to create either spacer assembly 30 or 40. The cartwheeling assembly process is time consuming and includes too many manual steps to be easily automated. It is thus desired in the art to provide a nonmetallic, desiccant-carrying spacer member that may be combined with a first spacer member (such as the metal spacer frame segments from the Glass Equipment Development linear system or the metal INTERCEPT® spacer member) to form a spacer assembly that eliminates metal-to-glass contact. It is particularly desirable to provide such a spacer assembly that may be fabricated in a linear arrangement to custom lengths so that the spacer assembly may be simply folded into a frame and used to form the glazing unit.